The present invention relates to an optical length adjusting device, and more particularly to an optical length adjusting device which is used in a scanner for adjusting the focus for multiple resolutions.
Along with the popularization of personal computers (PC), various models of peripheral appliances have been put on the market, and the demand has been on the rise. One of the examples is the optical scanner. Optical scanners are used to capture and digitize images and have different types to meet the market demand for different users. When a scanner is operated in high resolution, it can capture a higher quality image, but its scanning view will be smaller and its scanning speed will be slower than one operated at low resolution. However, users do not always require the finest high-resolution scanning process at all times, therefore, with the consideration of cost and utility, a scanner with high/low resolution has been introduced.
In other words, under the condition of not increasing the amount of the sensor pixel of a CCD, when a user requires high-resolution scanning, the area being scanned is limited to a smaller area and focused by a first image lens to a CCD; conversely, when a low-resolution scanning is required, a second image lens will be used to focus a larger area of the scanned image to project it to the CCD. However, since the focuses of the first and second lenses are different, and also the distances between the scanned object and the focusing lens, therefore, two sets of optical paths for different optical lengths shall be required, as in the prior art shown in FIGS. 1 and 2. This prior art was disclosed in U.S. Pat. No. 5,705,805 issued on Jan. 6, 1998.
As shown in FIG. 1, when a scanned image is projected from the position 80, it is reflected by mirrors 74, 76, 72 and 70 and into a focusing lens 62 to form a first path and optical length 152 between the position 80 and the focusing lens 62. As shown in FIG. 2, when said scanned image is projected from the position 80, it is reflected by mirrors 74, 72 and 70 and into the focusing lens 64 to form a second path and optical length 158 between the position 80 and the focusing lens 64. This second path does not travel via the mirror 76, and it is achieved by rotating the angle of the mirror 74.
However, the prior art employs two optical paths to accomplish the objective of different optical paths to suit different lenses. The intention is to combine the two high/low resolution optical paths and align them with the axis of the lens. Therefore, in case there is any deviation from the combination of the two high/low resolution optical paths, it will influence the quality of the image. On the other hand, since it requires numerous components for forming the two types of optical lengths and paths, especially when assembling in a limited space, there could be error in the combination due to sophisticated assembling processes, which could influence the quality of image. To reduce the number of components, we may use a movable reflecting mirror. However, the driving mechanism will become more sophisticated, if it meets different demands of reflecting documents and transmissive documents by incorporating other optical paths. Therefore, to meet the trend of high/low resolution scanning capabilities, and the design of a various-type documents scanning mechanism, there is a need for a unit equipped with a minimum number of optical components to achieve the purpose of adjusting optical length.